Fires Have Made California Cities Top World’s List of Most Polluted Places

San Francisco, Stockton and Sacramento were recorded as the world’s three “most polluted cities” on Friday due to the wildfires raging in northern California, CNN reported on Sunday.

Data from organizations that monitor air quality worldwide showed that the massive blazes had caused those parts of California to have worse air than the areas that usually top the most problematic international smog spots in India and China.

The problem has become so bad that schools and public transportation shut down in many of the areas.

“It appears to be the worst air quality ever experienced in San Francisco,” said University of Washington Prof. Dan Jaffe, who described the situation as “an air quality emergency.”

Experts said the smoke could destroy decades of progress on pollution, with Harvard University Prof. Daniel Jacob telling CNN that “We have made tremendous efforts and investment to clean up our air with considerable benefits for public health. But now it’s like we’re getting stabbed in the back with those wildfires.”

Jacob said that particulate matter (PM) is the “number one environmental killer in the world,” emphasizing that “the levels that are present in those areas affected by wildfires are like you might expect on a very polluted day in China or India.”

Jacob said “We give people advice to say indoors and to reduce exercise and things like that, but those don’t mitigate the problem too much,” especially in places like San Francisco where many people don’t have air conditioning.

He explained that without any sort of “controlled system” to filter air, a building doesn’t give much protection against PM.

However, when air is properly filtered, people can “reduce their PM exposure by about 90 percent” by being inside, he said.